The present invention relates to truck-mounted brakes for a railroad vehicle and more particularly to an improved method of replacing packing cups on a single actuator-slack adjuster while mounted to truck mounted brakes.
The accepted truck mounted brakes throughout the railroad industry approved by AAR is a double actuator system known as NYCOPAC sold by New York Air Brake Corporation and its equivalent WABCOPAC sold by Westinghouse Air Brake Corporation. Two actuators are used, one connected to each brake beam on opposite sides of the center axis. An example of the structure is illustrated in U.S. Pat. No. 3,499,507. The next generation of truck mounted brake includes a single actuator, truck mounted brake assembly known as NYCOPAC II and WABCOPAC II. This structure includes a single actuator with a pair of force transmitting arms and a lever connected to the opposite brake beam. A typical example of this structure is illustrated in U.S. Pat. No. 4,793,446.
As illustrated in U.S. Pat. No. 3,499,507, the slack adjuster is provided on the opposite end of the force transmitting device from the actuator and in the opposing brake beam. The NYCOPAC and WABCOPAC have no slack adjuster. In the single actuator system illustrated in U.S. Pat. No. 4,793,446 the slack adjuster is on the return force transmitting device. It is important that the force transmitting elements and the slack adjuster do not intersect the openings in the bolster for the various angular positions of the force transmitting elements.
The single actuator, truck mounted brake provides a force generated by the brake cylinder multiplied by a factor of four. This system is very effective as a force generated by the brake cylinder is transferred to the center of the arc of each of the shoes equally. The center of the force in the middle of each of the shoes eliminates wasted torsional components that exist in other systems.
The NYCOPAC II including a double acting slack adjuster brake cylinder having air on one side of the piston to apply the brakes and a spring return. The hand brake is connected to the piston directly by a series of cables, rods and chains. Since the hand brake worked directly on the piston, the slack adjuster operated the same when actuated by air as well as the hand operated brakes. In a single actuator system illustrated in U.S. Pat. No. 4,793,446, wherein the slack adjuster is in the return force transmitting element or device, the hand brake has been applied at the output of the actuator prior to the slack adjuster. This structure, as illustrated in U.S. Pat. Nos. 4,771,686 and 5,069,312, applies a single force in a common direction to the slack adjuster and thus is similar to operation to the NYCOPAC II without the use of cables or connection to the piston itself, internal the brake cylinder.
When one attempts to incorporate a hand brake connected to the output of the actuator where the actuator includes the slack adjuster thereby eliminating the cables from the NYCOPAC II, dangerous situations may be produced. The pulling forces produced by the hand brake are substantially larger than the pushing force produced by the pneumatic actuated piston. This could detrimentally affect and possibly destroy the slack adjuster. Also, if the actuator is not operated by air after replacement of brakes, the elements within the slack adjustor are not in their appropriate position and an application of the hand brake would not produce a slack adjusting operation. Thus, either the hand brake will not apply the brakes in one situation or the hand brake will produce a force which could destroy or severely damage the slack adjuster in the other extreme. The single actuator-slack adjuster of the aforementioned application provides a solution to these problems.
The packing cup of the piston of the single actuator must be changed approximately every five years. Where a single actuator is used for truck mounted brakes, the cylinder housing for the piston is usually connected at both ends between the actuator system for the brake beams and the brake beam itself. Thus, to obtain access to the packing cup, the actuator has to be removed from the brake beam or truck. This involves a substantial amount of time in removing the actuator in addition to replacement of the cup.
Since the actuator generally includes a spring biasing the piston to a released position, dismantling of the cylinder housing for the piston is tricky. Replacement of the packing cup is also more difficult when the actuator piston is also integral with the housing for the slack adjuster. The inter-relationship of the slack adjuster to the piston must be taken into account. Also, the actuator is generally positioned between a brake beam and the axle. This limits the space or clearance available between the brake beam and axle to maneuver the actuator or portions thereof for removal and replacement.
Thus, it is an object of the present invention to provide a method for replacing the packing cup of an actuator without removing the actuator from the brake beam or truck.
Another object of the present invention is to provide a unitary slack adjuster and actuator which is capable of having its packing cup replaced while mounted to a brake beam or truck.
These and other objects are achieved by moving a piston and a force transmitting element connected to the piston by a slack adjuster to a locking position. The piston and force transmission elements are locked in the locking position which preferably is displaced from the brake released position. This increases the spacing between the piston and an adjacent axle. A portion of the cylinder surrounding the piston is removed from the housing which is connected to the brake beam or truck and the packing cup is replaced. The cylinder portion is then replaced on the housing and the piston force transmission elements are unlocked and the piston force transmission are allowed to return to their released position.
The piston and force transmission elements are removed from their brake released position towards the brake applied position so as not to activate the slack adjuster during this movement. As an initial step prior to moving the piston slack adjuster element from the released position towards the brake applied position, the slack adjuster is actuated to shorten its length. This allows the subsequent moving step to have its maximum length of travel without applying the brakes and increases the distance between the brake beam and the axle.
In a first embodiment, the piston is locked to the housing. The piston includes a rod sliding in a bore in the housing and the rod to the housing. The rod includes a transverse slot and the housing includes an aperture intersecting the bore. A detent pin is inserted through the aperture and into the slot when they are aligned in the locking position so as to lock the pin to the housing. As an alternative to the transverse slot in the rod, the aperture that intersects the bore of the rod is threaded and a set screw in the thread aperture would engage the rod and lock the piston to the housing.
An improved integral brake actuator/slack adjuster unit includes the slot in the rod of the piston and the aperture intersecting the bore so that they can be used with the detent pin or a threaded aperture and set screw.
In the second embodiment of the present method, the force transmission element is locked to the truck, or a second brake beam. This includes inserting a block between a lever mounted to a second beam and connected to the force transmission element and the second brake beam to hold the force transmission element and the connected piston displaced from the brake released positions and locked in a first direction. In this embodiment, the force transmission element is again moved towards its brake applied position during unlocking to allow removing of the block. It should also be noted that the block defines the locking position for the first embodiment using the detent pin or screw and may be used in combination therewith to lock the piston and the force transmission elect.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.